Replication of versions of an object from a source storage to a target storage

ABSTRACT

Provided are a computer program product, system, and method for replication of versions of an object from a source storage to a target storage. A source retention policy indicates at least one source retention requirement to determine when to expire versions of an object at the source storage and a target retention policy indicates at least one target retention requirement to determine when to expire versions of the object at the target storage. The source and target retention requirements for versions of the object are different. The source retention policy is used to expire at least one version of the object at the source storage to satisfy the at least one source retention requirement. A number of the versions of the object maintained at the source storage and target storage differ due to the different source and target retention requirements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a computer program product, system, and method for replication of versions of an object from a source storage to a target storage.

2. Description of the Related Art

Data replication is used to replicate data belonging to multiple client systems from one server to another server, so that if the main source server to which data is being backed-up goes down, the clients can recover their data from the replication site. A storage-management server such as Tivoli® Storage Manager (TSM) stores data objects in one or more storage pools and uses a database for tracking metadata about the stored objects. (Tivoli is a trademark of International Business Machines Corporation worldwide). The storage management server may replicate the data objects to a remote location for disaster recovery purposes. Some of the methods used to transfer data to a remote location include physically transporting tapes containing copies of the data from the source site to the disaster recovery site, electronically transmitting the data (TSM export/import) or using hardware replication of the source site disk storage to create a mirror of the data.

There is a need in the art for improved techniques for replicating objects from one server to another.

SUMMARY

Provided are a computer program product, system, and method for replication of versions of an object from a source storage to a target storage. A source retention policy indicates at least one source retention requirement to determine when to expire versions of an object at the source storage and a target retention policy indicates at least one target retention requirement to determine when to expire versions of the object at the target storage. The source and target retention requirements for versions of the object are different. A new version of the object is replicated from the source storage to the target storage. The source retention policy is used to expire at least one version of the object at the source storage to satisfy the at least one source retention requirement. A number of the versions of the object maintained at the source storage differs from a number of the versions of the object maintained at the target storage due to the different source and target retention requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a replication environment in which embodiments are implemented.

FIG. 2 illustrates an embodiment of object information.

FIGS. 3a and 3b illustrate an embodiment of operations to replicate versions of an object from a source storage to a target storage.

FIG. 4 illustrates an embodiment of operations to expire versions of an object on the source storage.

FIG. 5 illustrates an embodiment of operations to process replicated versions of an object at the target storage.

FIGS. 6, 7, and 8 illustrate examples of replicating and expiring versions of objects in accordance with described embodiments.

FIG. 9 illustrates a computing environment in which the components of FIG. 1 may be implemented.

DETAILED DESCRIPTION

Each time a backup of the same object is performed, a new version is created. Retention policies indicate how many of the older versions to maintain, and may specify an age limit and retention number limit of versions of the object to maintain. Described embodiments provide techniques for replicating versions of an object from a source storage to a target storage and expiring the versions on the source storage using a source retention policy and target retention policy specifying different source and target retention number of versions that may be maintained on the source and target storages, respectively.

In the described embodiments, the source and target retention policies may have different retention policies, such as indicating different source and target retention number of versions of the object to retain, respectively. Further, the target retention policy may be used to determine a number of unreplicated versions of the object at the source storage to replicate to the target storage and to determine the number of unreplicated versions of the object to expire when the source and target retention numbers of versions are different.

Allowing for different retention policies at the source and target may be advantageous in a situation where a source storage has limited storage resources for production and backup versions and a target storage at a remote site has more ample storage, such that different retention policies are optimal for reflecting the need to limit versions of an object at the source production site and allowing more versions to be retained on the target storage. Alternatively, different retention policies may be preferable when the source storage can retain more versions than the target storage. Another retention policy may specify to only maintain the active version on the target storage 110 a for disaster recovery.

FIG. 1 illustrates an embodiment of a replication environment 100 having a source server 104 a and target server 104 b including a source replication manager 106 a and target replication manager 106 b, respectively, to replicate versions of an object 108 a at a source storage 110 a to copies of the versions of the object 108 b at target storage 110 b. The replication may be performed on behalf of a client node (not shown) connected to the source server 104 a to replicate objects owned by the client node. The source server 104 a and target server 104 b maintain versions of one or more data objects as defined in the object information 200 a and 200 b, respectively.

The source server 104 a maintains a source retention policy 114 a that may indicate at least one of a source age limit and source retention number limit of versions of an object to retain at the source storage 110 a, and may specify the number of active and inactive versions to retain. An active version is the most recent version of an object still resident on the protected client system, whereas inactive versions are previous versions that have been modified or deleted from the client system. The target server 102 b maintains a target retention policy 114 b that may indicate at least one of a target age limit and target retention number limit of the active and inactive versions to retain at the target storage 110 b. The source server 104 a may maintain a copy of the target retention policy 114 b′ to use to determine which versions of the object 108 a to replicate and expire.

The source server 104 a and target server 104 b maintain object information 200 a and 200 b, respectively, having information on the versions of an object maintained in their respective storages 110 a, 110 b. The source server 104 a may further maintain a copy of the target object information 200 b′ to use to determine which versions of the object 108 a to replicate. The source server 104 a may obtain the target object information 200 b and retention policy 114 b by querying the target server 104 b or by the target server 104 b forwarding such information when there are changes to the target retention policy 114 b and target object information 200 b.

Although FIG. 1 is described with respect to versions of one object, the source 110 a and target 110 b storages may maintain versions of multiple objects that are replicated.

The source server 104 a and target server 104 b may be implemented in separate computer devices that communicate over a network, such as a local area network (LAN), storage area network (SAN), wide area network (WAN), etc. In further embodiments, the source server 104 a and target 104 b may be implemented on one or two computer systems. If the source server 104 a and target server 104 b are in the same system, then they may communicate over a bus or via memory.

The source 110 a and target 110 b storages may each be implemented in one or more storage devices, or an array of storage devices configured as Just a Bunch of Disks (JBOD), Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID) array, virtualization device, tape storage, flash memory, etc. The storage devices may comprise hard disk drives, solid state storage device (SSD) comprised of solid state electronics, EEPROM (Electrically Erasable Programmable Read-Only Memory), flash memory, flash disk, Random Access Memory (RAM) drive, storage-class memory (SCM), etc., Phase Change Memory (PCM), resistive random access memory (RRAM), spin transfer torque memory (STM-RAM), conductive bridging RAM (CBRAM), magnetic hard disk drive, optical disk, tape, etc. Although a certain number of instances of elements, such as servers, storages, active and inactive copy relationships, etc., are shown, there may be any number of these components.

The source replication manager 106 a and target replication manager 106 b may comprise software programs in a memory executed by a processor. In an alternative embodiment, some portion or all of the programs 106 a, 106 b may be implemented in a hardware component, such as a dedicated integrated circuit, e.g., Application Specific

Integrated Circuit (ASIC), expansion card, etc.

Although the source replication manager 106 a and target replication manager 106 b are shown as separate components, in alternative implementations the functions performed by these components 106 a, 106 b may be implemented in a single program component in a single computer system or in more than two program components in more than two computer devices.

The source 106 a and target 106 b replication managers may be used by client nodes to recover objects as part of a restore operation.

FIG. 2 illustrates an instance of object information 200, that may be maintained in the source 200 a and target 200 b object information. The object information 200, may indicate an object identifier (ID) 202, a version number 204 of the object 202, indication 206 that the version is active or inactive, and for the source object information 200 a a replication field 208 indicating whether the version 204 of the object 202 has been replicated to the target server 104 b. The object information 200 a and 200 b may be implemented in a database, structured file, index, table, and other data structures known in the art.

FIGS. 3a and 3b illustrate an embodiment of operations performed by the source replication manager 106 a to replicate versions of an object 108 a from the source storage 110 a to the target storage 110 b to store as versions of the object 108 b. The replication (at block 300) may be initiated in response to creating a new active version, such as immediate replication when the object 108 a has changed, or after a number of new versions of the object have been created, such as periodic replication. If (at block 302) there is only one unreplicated version of the object 108 a that has not been replicated to the target storage 110 b, then the source replication manager 106 a replicates (at block 304) the new version of the object 108 a to the target storage 110 b. The source object information 200 a for the replicated version of the object is updated (at block 306) to indicate that the object was replicated, such as by updating the replicated field 208 to indicate the object 202 and version 204 was replicated. If (at block 308) the versions of the objects 108 a at the source storage 110 a do not satisfy the source retention policy 114 a, in terms of age limits of the objects and/or number limits of the versions, then the source replication manager 106 a expires (at block 310) any versions of the object 108 a necessary to satisfy the source retention policy 114 a. For example, any versions having an age exceeding an age limit and/or exceeding the source retention number limit may be deleted, such as by expiring oldest versions of the object first, e.g., First-In-First-Out (FIFO), as further described with respect to FIG. 5. If (from the no branch at block 308) the number of versions 108 a satisfies the source retention policy 114 a, then control ends.

If (at block 302) there are a plurality of unreplicated versions of the object, then control proceeds to block 312 et seq. in FIG. 3b to determine whether to replicate unreplicated versions in a manner that satisfies the target retention policy 114 b, such as an age limit and/or retention number limit. At block 312, a number to replicate is set to zero if there is a target retention number limit. A loop of operations is then performed for each unreplicated version of the object, from a newest one to oldest, i.e., LIFO. If (at block 316) the unreplicated version satisfies the age limit of the target retention policy 114 b′, which is also satisfied if there is no age limit, then if (at block 318) there is a target retention number limit, then the number of versions to replicate is incremented (at block 320). If (at block 322) the number to replicate at the source does not exceed the target retention number limit of the target retention policy 114 b′, then the version of the object is replicated (at block 324) to the target storage 110 b. If (at block 318) there is no target retention limit after the target age limit has been satisfied, then control proceeds to block 324 to replicate the object.

After all unreplicated versions have been considered (from block 326) or if the number to replicate exceeds the target retention policy number limit (from the yes branch of block 322) or if the unreplicated version does not satisfy the target age limit (from the no branch of block 316), then control proceeds to block 328 to stop considering further unreplicated versions and update the object information 200 to indicate that any unreplicated versions are replicated. The object information 200 may be updated by updating field 208 in the object information instance 200 _(i).

From blocks 316 and 322, further older unreplicated versions do not need to be considered because such further versions would not satisfy any target age and/or number limits of the target retention policy 114 b if they are not satisfied after considering a more recent unreplicated version of the object.

With the operations of FIGS. 3a and 3b , the source replication manager 106 a uses the target retention policy 114 b′ to determine whether unreplicated versions of the object should be replicated based on any target age limit and/or retention number limit specified in the target retention policy 114 b. If there is a retention number limit, then unreplicated versions will not be replicated if doing so would violate any target age limits or total retention number limits. The unreplicated versions may be considered from newest ones first, such that at any point if one of the target age and/or retention number limits would be exceeded, then no further unreplicated objects would be replicated if the previously considered newer version does not satisfy age and or total retention number limits of the target retention policy 114 b. In this way, if the source retention number of versions to have according to the source retention policy 114 a exceeds the target retention number limit, then the source replication manager 106 a replicates a number of at least one of the unreplicated versions of the object at the source storage to the target storage such that the replicated number does not exceed the target retention number limit. However, if the target retention number exceeds the source retention number, then the source replication manager 106 a replicates a number of at least one of the unreplicated versions of the object at the source storage such that the replicated number does not exceed the target retention number limit.

In this way the target retention policy 114 b is used by the source replication manager 104 a to determine a number of unreplicated versions of the object to replicate when there are a plurality of unreplicated versions of the object. With the operations of FIGS. 3a and 3b , a number of at least one of the unreplicated versions of the object at the source storage is replicated to the target storage such that the replicated number of the unreplicated versions of the object will be stored on the target storage according to the target storage policy. For instance, a number of at least one of the unreplicated versions of the object at the source storage is replicated such that the replicated number of the at least one of the unreplicated versions of the object does not exceed a target retention number limit of the target retention policy.

FIG. 4 illustrates an embodiment performed by the source replication manager 106 a, or some other component such as a source expiration manager, to expire versions of the object 108 a at the source storage 110 a. Upon initiating (at block 400) an expiration operation on the source storage 110 a, a loop of operations is performed at blocks 402 through 418 for each version of the object on the source storage, from the oldest one to most recent version. If (at block 404) the version does not need to be expired to satisfy the source retention policy 114 a, e.g., target age and/or retention number limits, then control ends. That is, if the oldest version number satisfies the policies, then expiration processing can end.

However, if the current oldest version being considered does not satisfy the source retention policy, i.e., is too old or too many versions on the source storage 110 a, then if (at block 406) the version is unreplicated, then the source replication manager 106 a determines whether the version satisfies a target age limit (if there is one). If (at block 408) the age limit is satisfied, which is also satisfied if there is no target age limit, and if (at block 410) there is a target retention number limit, then the source replication manager 106 a determines whether the total number of unreplicated versions on the source storage 110 a exceeds the target retention number limit. If (at blocks 408 and 410) the age limit is satisfied and there is no retention number limit or if (at block 412) the number of unreplicated versions does not exceed a target retention number limit, then the unreplicated object is not expired (at block 416) even if its presence violates the source retention policy 114 a requirements.

If the version is not unreplicated (from the no branch of block 406) or if the version does not satisfy the target age limit (from the no branch of block 408) or if the total number of unreplicated versions exceeds the target retention number limit (from the yes branch of block 412), then the version is expired (at block 414) to satisfy the source storage retention policy 114 a. From block 414, control proceeds to block 418 to consider the next oldest version of the object on the source storage 110 a.

With the operations of FIG. 4, unreplicated versions of the object on the source storage 110 a are expired to attempt to satisfy the source retention policy without expiring unreplicated objects that could be stored on the target storage according to the target retention policy. Unreplicated versions of the object are expired if the unreplicated version does not satisfy an age limit when included in the target retention policy 114 b and one of the unreplicated versions of the object is expired if a total number of unreplicated versions on the source storage exceeds a target retention number limit when included in the target retention policy 114 b. The unreplicated versions are not expired when they satisfy the age limit and/or the total number of unreplicated versions does not exceed the target retention number limit.

FIG. 5 illustrates an embodiment of operations performed by the target replication manager 106 b, or by the source replication manager 106 a, to process a replicated version of the object. Upon receiving (at block 500) the replicated version, the target replication manager 106 b stores (at block 502) the received replicated version of the object as object version 108 b in the target storage 110 b. The target replication manager 106 b expires (at block 506) any versions of the object necessary to maintain the target retention number of versions specified by the target retention policy, such as by expiring oldest versions of the object first, e.g., FIFO, and any versions not satisfying any target age limit.

With the described operations, separate source 114 a and target 114 b retention policies having different source and target retention numbers of version limits, respectively, may be provided to determine the number of versions to replicate to the target storage 110 b and to independently determine versions of the object 108 a and 108 b to expire, which may result in a different number of versions of the object on the source 110 a and target 110 b storages.

FIGS. 6, 7, 8, and 9 illustrate examples of the replication and expiration operations described above. In FIG. 6, the source retention policy 114 a is to keep one active and two inactive versions and the target retention policy 114 b is to keep one active and one inactive versions. A shown in FIG. 6, the replication always sends the new version of the object A1, A2 or A3, but the separate application of the retention policies 114 a and 114 b results in a different number of versions of the object on the source 110 a and target 110 b storages.

FIG. 7 illustrates an alternative example where the source retention policy 114 a is to keep one active and one inactive version and the target retention policy 114 b is to keep one active and two inactive versions. As shown in FIG. 7, the replication always sends the new version of the object A1, A2 or A3, but the separate application of the retention policies 114 a and 114 b results in a different number of versions of the object on the source 110 a and target 110 b storages.

FIG. 8 illustrates an example where the source retention policy 114 a is to keep two versions (one active and one inactive) and the target retention policy 114 b is to keep three versions (one active and two inactive versions). In FIG. 8, there are a plurality of unreplicated versions after the third version is stored—A3, A2, A1 after storing the third version. However, application of the source retention policy 114 a at expiration step 800 would otherwise expire A1, but the application of the expiration at step 800 leaves three versions A3, A2, A1 according to the operations of FIG. 4 to leave enough unreplicated versions to satisfy the target retention policy 114 b. After replicating all the unreplicated versions at replication step 802, the application of the source retention policy 114 a at expiration step 804 leaves only two versions A3 and A2, and three versions A3, A2, A1 on the target storage whose target retention policy 114 b permits three versions to be retained.

Described embodiments permit separate source and target retention policies that allow for different number of versions of an object to be maintained at the source and target storages. Further, the source and target retention policies may be used both to determine the number of unreplicated versions of an object on the source storage to expire as well as to replicate, in order to provide a sufficient number of unreplicated versions to the target storage when the target retention policy permits more versions than the source retention policy and to minimize the number of versions to replicate when the source retention policy permits more versions to be maintained than the target retention policy.

The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.

Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.

The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

The computational components of the computing environment 102, such as the source server 104 a and target server 104 b may be implemented in one or more computer systems, such as the computer system 902 shown in FIG. 9. Computer system/server 902 may be described in the general context of computer system executable instructions, such as program modules, being executed by a computer system. Generally, program modules may include routines, programs, objects, components, logic, data structures, and so on that perform particular tasks or implement particular abstract data types. Computer system/server 902 may be practiced in distributed cloud computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed cloud computing environment, program modules may be located in both local and remote computer system storage media including memory storage devices.

As shown in FIG. 9, the computer system/server 902 is shown in the form of a general-purpose computing device. The components of computer system/server 902 may include, but are not limited to, one or more processors or processing units 904, a system memory 906, and a bus 908 that couples various system components including system memory 906 to processor 904. Bus 908 represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 902 typically includes a variety of computer system readable media. Such media may be any available media that is accessible by computer system/server 902, and it includes both volatile and non-volatile media, removable and non-removable media.

System memory 906 can include computer system readable media in the form of volatile memory, such as random access memory (RAM) 910 and/or cache memory 912. Computer system/server 902 may further include other removable/non-removable, volatile/non-volatile computer system storage media. By way of example only, storage system 913 can be provided for reading from and writing to a non-removable, non-volatile magnetic media (not shown and typically called a “hard drive”). Although not shown, a magnetic disk drive for reading from and writing to a removable, non-volatile magnetic disk (e.g., a “floppy disk”), and an optical disk drive for reading from or writing to a removable, non-volatile optical disk such as a CD-ROM, DVD-ROM or other optical media can be provided. In such instances, each can be connected to bus 908 by one or more data media interfaces. As will be further depicted and described below, memory 906 may include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of embodiments of the invention.

Program/utility 914, having a set (at least one) of program modules 916, may be stored in memory 906 by way of example, and not limitation, as well as an operating system, one or more application programs, other program modules, and program data. Each of the operating system, one or more application programs, other program modules, and program data or some combination thereof, may include an implementation of a networking environment. The components of the computer 902 may be implemented as program modules 916 which generally carry out the functions and/or methodologies of embodiments of the invention as described herein. The systems of FIG. 1 may be implemented in one or more computer systems 902, where if they are implemented in multiple computer systems 902, then the computer systems may communicate over a network.

Computer system/server 902 may also communicate with one or more external devices 918 such as a keyboard, a pointing device, a display 920, etc.; one or more devices that enable a user to interact with computer system/server 902; and/or any devices (e.g., network card, modem, etc.) that enable computer system/server 902 to communicate with one or more other computing devices. Such communication can occur via Input/Output (I/O) interfaces 922. Still yet, computer system/server 902 can communicate with one or more networks such as a local area network (LAN), a general wide area network (WAN), and/or a public network (e.g., the Internet) via network adapter 924. As depicted, network adapter 924 communicates with the other components of computer system/server 902 via bus 908. It should be understood that although not shown, other hardware and/or software components may be used in conjunction with computer system/server 902. Examples, include, but are not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data archival storage systems, etc.

The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment” mean “one or more (but not all) embodiments of the present invention(s)” unless expressly specified otherwise.

The terms “including”, “comprising”, “having” and variations thereof mean “including but not limited to”, unless expressly specified otherwise.

The enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expressly specified otherwise.

Devices that are in communication with each other need not be in continuous communication with each other, unless expressly specified otherwise. In addition, devices that are in communication with each other may communicate directly or indirectly through one or more intermediaries.

A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary a variety of optional components are described to illustrate the wide variety of possible embodiments of the present invention.

When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the present invention need not include the device itself.

The foregoing description of various embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims herein after appended. 

What is claimed is:
 1. A computer program product for replicating objects from a source storage to a target storage, the computer program product comprising a computer readable storage medium having computer readable program code embodied therein that executes to cause operations, the operations comprising: providing a source retention policy indicating at least one source retention requirement to determine when to expire versions of an object at the source storage and a target retention policy indicating at least one target retention requirement to determine when to expire versions of the object at the target storage, wherein the source and target retention requirements for versions of the object are different; replicating a new version of the object to the target storage; and using the source retention policy to expire at least one version of the object at the source storage to satisfy the at least one source retention requirement, wherein a number of the versions of the object maintained at the source storage differs from a number of the versions of the object maintained at the target storage due to the different source and target retention requirements.
 2. The computer program product of claim 1, wherein the source and target retention requirements indicate at least one of a retention number of versions of the object to maintain and a retention age limit for the versions of the object, wherein the source and target storages do not retain more than the retention number of versions of the object when indicated in their respective source and target retention policies and wherein the source and target storages do not have versions of the object exceeding the retention age limit when indicated in their respective source and target retention policies.
 3. The computer program product of claim 1, wherein the using of the source retention policy to expire at least one version of the object at the source storage is performed in response to storing the new version of the object on the source storage, wherein the replication of the version of the object on the source storage to the target storage causes the expiration of at least one version of the object on the target storage according to the target retention policy.
 4. The computer program product of claim 1, wherein the using the source retention policy to expire at least one version of the object comprises expiring an oldest version of the object.
 5. The computer program product of claim 1, wherein the operations further comprise: determining that there are plurality of unreplicated versions of the object at the source storage that have not been replicated to the target storage; and replicating a number of at least one of the unreplicated versions of the object at the source storage to the target storage such that the replicated number of the unreplicated versions of the object will be stored on the target storage according to the target storage policy.
 6. The computer program product of claim 5, wherein the replicating the number of at least one of the unreplicated versions of the object is performed when a number of the versions of the object retained according to the source storage policy exceed a number of versions of the object retained according to the target retention policy.
 7. The computer program product of claim 5, wherein the operations further comprise: updating the object information to indicate all the unreplicated versions of the object as replicated in response to replicating the at least one of the unreplicated versions of the object.
 8. The computer program of claim 1, wherein the target storage policy specifies a target retention number limit, and wherein the replicating the new version of the object when there are a plurality of unreplicated versions of the object at the source storage that have not yet been replicated to the target storage further comprises: replicating a number of at least one of the unreplicated versions, including the new version, of the object at the source storage such that the replicated number of the at least one of the unreplicated versions of the object does not exceed the target retention number limit.
 9. The computer program product of claim 1, wherein the using the source retention policy to expire at least one version of the object when there are unreplicated versions of the object at the source storage that have not yet ben replicated to the target storage comprises: expiring unreplicated versions of the object on the source storage to attempt to satisfy the source retention policy without expiring unreplicated objects that could be stored on the target storage according to the target retention policy.
 10. The computer program product of claim 9, wherein the expiring unreplicated versions of the object on the source storage to attempt to satisfy the source retention policy comprises: expiring one of the unreplicated versions of the object if the unreplicated version does not satisfy an age limit when included in the target retention policy; and expiring the one of the unreplicated versions of the object if a total number of unreplicated versions on the source storage exceeds a target retention number limit when included in the target retention policy, wherein the unreplicated versions are not expired when they satisfy the age limit and/or the total number of unreplicated versions does not exceed the target retention number limit.
 11. A system for replicating objects from a source storage to a target storage, comprising: a processor; and a computer readable storage medium having computer readable program code that when executed by the processor performs operations, the operations comprising: providing a source retention policy indicating at least one source retention requirement to determine when to expire versions of an object at the source storage and a target retention policy indicating at least one target retention requirement to determine when to expire versions of the object at the target storage, wherein the source and target retention requirements for versions of the object are different; replicating a new version of the object to the target storage; and using the source retention policy to expire at least one version of the object at the source storage to satisfy the at least one source retention requirement, wherein a number of the versions of the object maintained at the source storage differs from a number of the versions of the object maintained at the target storage due to the different source and target retention requirements.
 12. The system of claim 11, wherein the source and target retention requirements indicate at least one of a retention number of versions of the object to maintain and a retention age limit for the versions of the object, wherein the source and target storages do not retain more than the retention number of versions of the object when indicated in their respective source and target retention policies and wherein the source and target storages do not have versions of the object exceeding the retention age limit when indicated in their respective source and target retention policies.
 13. The system of claim 11, wherein the operations further comprise: determining that there are plurality of unreplicated versions of the object at the source storage that have not been replicated to the target storage; and replicating a number of at least one of the unreplicated versions of the object at the source storage to the target storage such that the replicated number of the unreplicated versions of the object will be stored on the target storage according to the target storage policy.
 14. The system of claim 11, wherein the target storage policy specifies a target retention number limit, and wherein the replicating the new version of the object when there are a plurality of unreplicated versions of the object at the source storage that have not yet been replicated to the target storage further comprises: replicating a number of at least one of the unreplicated versions, including the new version, of the object at the source storage such that the replicated number of the at least one of the unreplicated versions of the object does not exceed the target retention number limit.
 15. The system of claim 11, wherein the using the source retention policy to expire at least one version of the object when there are unreplicated versions of the object at the source storage that have not yet ben replicated to the target storage comprises: expiring unreplicated versions of the object on the source storage to attempt to satisfy the source retention policy without expiring unreplicated objects that could be stored on the target storage according to the target retention policy.
 16. A method for replicating objects from a source storage to a target storage, comprising: providing a source retention policy indicating at least one source retention requirement to determine when to expire versions of an object at the source storage and a target retention policy indicating at least one target retention requirement to determine when to expire versions of the object at the target storage, wherein the source and target retention requirements for versions of the object are different; replicating a new version of the object to the target storage; and using the source retention policy to expire at least one version of the object at the source storage to satisfy the at least one source retention requirement, wherein a number of the versions of the object maintained at the source storage differs from a number of the versions of the object maintained at the target storage due to the different source and target retention requirements.
 17. The method of claim 16, wherein the source and target retention requirements indicate at least one of a retention number of versions of the object to maintain and a retention age limit for the versions of the object, wherein the source and target storages do not retain more than the retention number of versions of the object when indicated in their respective source and target retention policies and wherein the source and target storages do not have versions of the object exceeding the retention age limit when indicated in their respective source and target retention policies.
 18. The method of claim 16, further comprising: determining that there are plurality of unreplicated versions of the object at the source storage that have not been replicated to the target storage; and replicating a number of at least one of the unreplicated versions of the object at the source storage to the target storage such that the replicated number of the unreplicated versions of the object will be stored on the target storage according to the target storage policy.
 19. The method of claim 16, wherein the target storage policy specifies a target retention number limit, and wherein the replicating the new version of the object when there are a plurality of unreplicated versions of the object at the source storage that have not yet been replicated to the target storage further comprises: replicating a number of at least one of the unreplicated versions, including the new version, of the object at the source storage such that the replicated number of the at least one of the unreplicated versions of the object does not exceed the target retention number limit.
 20. The method of claim 16, wherein the using the source retention policy to expire at least one version of the object when there are unreplicated versions of the object at the source storage that have not yet ben replicated to the target storage comprises: expiring unreplicated versions of the object on the source storage to attempt to satisfy the source retention policy without expiring unreplicated objects that could be stored on the target storage according to the target retention policy. 